Ceramic fiber-ceramic matrix composites offer unequaled high-temperature performance and stability in oxidizing environments; however, the fabrication of strong, tough composites is a difficult task and often an expensive one. Generally, the fiber-reinforcement of otherwise brittle ceramic materials offers significant opportunities to toughen the brittle matrix; therefore, fiber preforms are used as starting material for incorporation within a surrounding ceramic matrix. The same also generally applies to carbon and metal matrices.
A number of techniques have been developed for incorporating a carbon, a metal or a ceramic matrix into a fiber preform, which techniques include filament-winding through a slurry of the matrix material, chemical vapor deposition or infiltration (CVD or CVI), and sol-gel infiltration. In passing filament material through a slurry of the matrix material prior to winding, only a relatively small amount of the matrix material adheres to the filaments. CVI or CVD is a notoriously slow process, often being measured in days, and it is expensive for such reason and because it traditionally requires special molds or supporting structures. More conventional ceramic processing techniques, such as slip casting and/or vacuum casting, followed by hot-pressing have not provided adequate penetration of the matrix material, particularly crystalline matrix material having a relatively high melting point, within the interstices of preforms made with reinforcing fibers, thereby leaving undesirably large amounts of void volume in the resultant product. Fiber-metal composites have been made by electrodepositing a metal matrix onto a cathode from an agitated bath containing whiskers of Al.sub.2 O.sub.3 or SiC fibers which become embedded therewithin, as shown in U.S. Pat. No. 3,498,890; however, there are limits to composite strengths that are obtained using such a process. An improvement of such a process using centrifugal force is shown in U.S. Pat. No. 3,716,461, but this process is complicated and still limited to the use of short fibers.
Certain matrix materials can be advantageously supplied by organic precursors, and resinous materials, such as synthetic organic polymers either in the form of fine particles or liquid resins, have more recently been employed for this purpose. However, liquid-phase impregnation utilizing either thermosetting resins or pitch-based coal tars, which are then pyrolyzed to form silicon carbide, silicon nitride, carbon or the like to provide matrix material, have relatively low solids yields following pyrolysis; thus, such liquid impregnations necessitate at least about 3 processing cycles to achieve composite densities of greater than 80%. Accordingly, manufacturing is complicated and relatively expensive because of the repetitive impregnation and pyrolysis cycles that are required.
As a result, more efficient methods continue to be sought for making relatively dense, fiber-reinforced carbon, ceramic and metal matrix composite materials.